Kitten food does have higher calaries. It's usually recommended for pregnant and nursing moms. Also, canned food generally has a higher fat content than dry. If possible I would suggest getting a fecal sample and have it tested for worms.
I don't think I'll be able to find a fecal sample of a feral cat.
But maybe I'll speak to my vet and see if I can get her worm medicine just in case she does have worms (if it won't harm her if she doesn't have worms)
I am going to continue to feed her some kitten food and see if that does anything. I feel so bad for her she is so tiny..... her litter was born about 8 weeks ago.